Osteoarthritis, also known as degenerative arthritis or degenerative joint disease, is the most common form of arthritis, affecting millions of people around the world. It is characterized by cartilage breakdown, subchondral sclerosis, osteophyte formation, and alterations to the joint capsule, resulting in degradation of the joints. Osteoarthritis is age-related. Physician-diagnosed arthritis occurs in more than 50% of adults older than age 65 years and in more than 30% of adults aged 45-64 years. Valdes et al., Best practice & Research Clinical Rheumatology, 24(1):3-14; 2010.
Interleukin IL-20 (IL-20) is a member of the IL-10 family, which includes IL-10, IL-19, IL-20, IL-22, IL-24, and IL-26. Blumberg, et al., 2001, Cell 104:9-19; Pestka et al., 2004, Annu Rev Immunol 22:929-979. IL-20 is expressed in monocytes, epithelial cells, and endothelial cells and acts on multiple cell types by activating a heterodimer receptor complex of either IL-20R1/IL-20R2 or IL-22R1/IL-20R2. Dumoutier, et al., 2001, J Immunol 167:3545-3549). IL-20 was found to be involved in various inflammatory diseases, such as psoriasis (Blumberg et al., 2001; Sa et al., 2007, J Immunol 178:2229-2240; and Wei et al., 2005, Clin Immunol 117:65-72), rheumatoid arthritis (Hsu, et al., 2006, Arthritis Rheum 54:2722-2733), atherosclerosis (Caligiuri, et al. 2006, Arterioscler Thromb Vasc Biol 26:1929-1930; and Chen et al., 2006, Arterioscler Thromb Vasc Biol 26:2090-2095), ischemic stroke (Chen et al., 2009, J Immunol 182:5003-5012), and renal failure (Li et al., 2008, Genes Immun 9:395-404). See also Wei et al., 2006, J Biomed Sci 13:601-612.